1. Field of the Invention
The present invention relates, in general, to external fixators for securing one or more elements and, more specifically, to an improved geared bar and carriage combination for orthopedic external fixators that allows controlled, independent translation of two or more carriages.
2. Background Art
In the practice of medicine, it is sometimes desirable to treat certain injuries or conditions with an external frame that is attached to the boney skeleton with threaded and/or smooth pins and/or threaded and/or smooth and/or beaded wires. Such constructs are commonly referred to as orthopedic external fixators or external skeletal fixators. These external fixators may be utilized to treat acute fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, nonunion of the skeleton when bones have not healed, malunion whereby broken or fractured bones have healed in a malposition, congenital deformities whereby bones develop a malposition, and bone lengthening, widening, or twisting.
External fixator flames vary considerably in design and capabilities, and may include multiple or single bars or rods, and a plurality of clamps or connectors for adjustably securing the bars to pins or wires which are, in turn, joined to the boney skeleton. The pins or wires may extend completely through the boney skeleton and out each side of the limb or may extend through the boney skeleton and out only one side of the limb. Pins which extend completely through the boney skeleton and out both sides of the limb are commonly referred to as "transfixation pins." Pins which extend through the boney skeleton and out only one side of the limb are commonly referred to as "half pins." Materials for frames also vary, including metals, alloys, plastics, composites, and ceramics. External fixators vary in their ability to accommodate different spatial relations between each pin and bar, etc.
Mears, U.S. Pat. No. 4,620,533, issued Nov. 4, 1986, discloses an orthopedic external fixator including a plurality of transfixation pins 1, an elongated bar 2, and a plurality of pin-to-bar clamps 3 for adjustably attaching the pins 1 to the bar 2. The pin-to-bar clamps 3 including articulating balls 11 for holding the pins 1 and the bar 2 when thumbscrews or the like are tightened. In addition, Mears discloses a bar-to-bar clamp for allowing a second elongated bar 2A to be clamped relative to the bar 2.
In the course of treatment with external fixation, it is sometimes desirable or preferable to translate one or more bone fragments or to lengthen bones along an axis parallel to the axis of an external fixator bar. During such controlled translation or movement, it is deskable to maintain or control the other spatial relations of each fragment.
Ettinger, U.S. Pat. No. 2,250,417, issued Jul. 22, 1941, discloses an orthopedic external fixator for fracture reduction and retention including an elongated bar 1, a plurality of elongated threaded pins 36 for transfixing bone elements, a first connector or head 2 attached to one end of the bar 1 for joining a pair of the pins 36 to the bar 1, and a second connector or sleeve 5 slidably positioned on the bar 1 for connecting another pair of the pins 36 to the bar 1. A portion of the bar 1 is externally threaded and two nuts 3, 4 are screwably mounted on the bar 1, one on either end of the sleeve 5, so that proper rotation of the nuts 3, 4 will cause the sleeve 5 and associated pins 36 to move along the bar 1. The bar 1 has either a circular cross section with a longitudinal keyway for receiving a key 7 of the sleeve 5 (see FIG. 3), or a square cross section with rounded, threaded corners 9 (see FIG. 4) in which case the sleeve 5 is provided with a square bore to hold the sleeve 5 against rotation on the bar 1. The threads on the bar 1 and the threaded apertures through the nuts 3, 4 are arranged concentric with the longitudinal axis of the bar 1.
Anderson, U.S. Pat. No. 2,391,537, issued Dec. 25, 1945, discloses an orthopedic external fixator for fracture reduction including a pair of hollow robes 20, 21 telescopically joined together, a plurality of pins 15 for transfixing bone elements, a first fixation unit A slidably mounted on the tube 21 for connecting a pair of the transfixion pins 15 to the tube 21, and a second fixation unit B attached to the end of the tube 20 for connecting a pair of the transfixation pins 15 to the tube 20. The tube 20 is telescopically mounted within the tube 21. A threaded adjusting shaft 25 is mounted within the tubes 20, 21 and can be manually rotated by way of a wrench head 30 located at the outer end of the tube 21. Rotation of the shaft 25 causes a nut 32 nonrotatably located within the tube 20 to move longitudinally along the shaft 25. Coil springs 34 located within the tubes 20, 21 on either side of the nut 32 transfer longitudinal movement of the nut 32 to the tubes 20, 21 while permitting a certain desired yielding and eliminating any perfectly solid and hard contact.
Nothing in the known prior art discloses or suggests the present invention. More specifically, nothing in the known prior art discloses or suggests an external fixator including an elongated bar; a first carriage means mounted on the bar for securement to a first element; a second carriage means mounted on the bar for securement to a second element; and drive means for driving the first and second carriage means along the length of the bar independent of one another.